Quality Scan: Thoughts About Gages
While working with a major automobile manufacturer recently, it came to light that there is an evolving corporate philosophy that is affecting Gage Departments, and it's a source of some friction between gage engineers and manufacturing engineers. It is no surprise that, like every enterprise on the face of the earth these days, auto companies are trying to cut costs and the mandates coming down from above—if that's what they are—have to do with cost cutting.
The first is directed at design-and-build hard gages. Top management appears to be looking for solutions that are flexible, reuseable, and require little energy, yet hard gages require a big investment and are single-purpose devices.
The traditional "dog-house" gage is a good example of how things have been done for years. To check size and position of holes in a block or head, for example, the part is placed into the gage, an actual wrap-around housing structure with precision bushings through which "sweep" gages are manually positioned and rotated, to obtain the size and true position of holes. These are custom gages that are initially very expensive to purchase, require very expensive precision setting masters that must be certified, and are essentially purpose-made, such that any engineering change to the part requires sometimes-costly gage redesign and modification, often with changes to the setting masters as well. Lead times can be quite long. While some hard gages are automated, many are hand-operated, so operators can exert some influence over results. Many often include pneumatically operated functions or air gages, but more on that later.
On the plus side, hard gages are usually durable in the production environment, easy to understand, and efficient to use, albeit with limited data-collecting capability (an operator may not always follow the same sequential steps, for example, or remember to hit the "Record" button).
A CMM is an example of a gaging device that is very flexible and eminently reuseable by reprogramming. However, the typical CMM today is an air-bearing instrument that is generally not thought of as rugged enough for an engine plant floor, unless it's placed inside a protective enclosure. CMMs have a big footprint, and real estate is at a premium in most factories. Also, they are generally slow when compared to hard gages. Factory personnel often talk about the queue in front of the nearest CMM, and some programs can run for a half hour to an hour.
Data collection in today's auto factories calls for a unique identity for every component of every single feature measured on every part made; for example: plant ID, line ID, part number, operation number, module number, right hand or left hand, feature number, Y-axis location, date, and time. This absolutely calls for digital devices, meaning that hand tools, manual operations, and paper entries are fading fast. CMMs can do this work elegantly, but hard gages pose more challenges.
A second directive targets anything using compressed air. A reliable source says that eliminating compressed air would save approximately $120,000 per year per plant. Air gages are left bleeding air 24 hr/day because shutting them down often causes plugging, temperature, and calibration problems. The same can be said for CMMs. Whether on all the time or shut down, these instruments consume huge amounts of compressed air every year, and the push is in place to find nonpneumatic substitutes.
Why is there friction between gage engineers and manufacturing engineers? In the view of gage engineers, who are trying to push through some of these changes, the MEs are resisting! They like the comfort of the way things have been done. Right or wrong, changes always bring uncertainty.
For gage makers and CMM suppliers alike, these directives are creating new opportunities and a changing marketplace in automotive plants. There appears to be emerging demand for smaller, faster, more rugged nonpneumatic CMM-like devices. They need to be flexible, able to be modified easily, adaptable to the next program, or suited to mixed production. They need to be lower in cost, and offer plug-and-play ease of implementation and swap-out serviceability. Indeed, something akin to programmable fixture gages may be the ideal solution.
When a new engine program can cost a half-billion dollars, it is at least encouraging that even a savings of $120,000 per year is getting attention at the top. That it involves savings in energy is even more telling. It's do or die in the car-making business.
This article was first published in the July 2010 edition of Manufacturing Engineering magazine.